1. Field
The present invention relates to image forming apparatuses, and particularly to an electrophotographic image forming apparatus comprising a plurality of exposure devices each having a plurality of light-emitting points arranged in a main scanning direction.
2. Description of Related Art
In an electrophotographic image forming apparatus, a photoconductor is exposed to light to form an electrostatic latent image on the photoconductor. In recent years, an exposure device including an exposure head having a plurality of light-emitting points, as implemented by light-emitting diodes (LEDs) or the like, arranged in a main scanning direction (i.e., the direction perpendicular to the direction of transport of a sheet on which an image is to be formed) has been provided for use in this exposure process.
In a color image forming apparatus, a plurality of such exposure heads are provided for a plurality of print colors such as cyan, magenta, etc. In order to prevent displacements of images foamed by the exposure heads, a color displacement correction may be performed.
The exposure head is typically configured to include a plurality of light-emitting chips arranged in the main scanning direction on a circuit board, and each light-emitting chip may be an LED array chip fabricated through a semiconductor process in which a plurality of LEDs as light-emitting elements are arranged precisely in a single row and packaged in a single semiconductor chip. To be more specific, the LED array chips are arranged in the main scanning direction on the circuit board in such a manner that adjacent LED array chips are in positions shifted from each other in a sub scanning direction that is perpendicular to the main scanning direction so as to prevent a gap in the main scanning direction from being left between a light-emitting point at an end of one chip and a light-emitting point at an opposite end (closer to the one chip) of another chip adjacent to the one chip.
Although each LED array chip fabricated through the semiconductor process has a plurality of light-emitting points very precisely aligned thereon, some error would be introduced in the assembly process for mounting the LED array chip on the circuit board. Moreover, there would also be an error introduced in the assembly process for mounting the exposure head to the body of the image forming apparatus. As a result, when a plurality of exposure heads are activated so that light is emitted from the same number of light-emitting points in all the exposure heads, regions on the photoconductor exposed to light emitted from the exposure heads would disadvantageously be misaligned with each other in the main scanning direction.
Under the circumstances, there is a need to provide an image forming apparatus which can achieve neat alignment in the main scanning direction of regions on a photoconductor exposed to light emitted from a plurality of exposure heads, whereby a quality color image can be formed.
The present invention has been made in an attempt to address the aforementioned problem in prior art.